As indicated in our last progress report, we isolated from the monkey brain a cDNA containing an open reading frame which encodes 91 amino acids with no significant homology to any other known protein. Northern blot analysis of different brain regions demonstrated that the novel cDNA (termed MK-14) encodes a ~1.8 kb mRNA, highly expressed in the striatum, hippocampus, thalamus and cerebral cortex. The abundance of this mRNA, was found to decrease markedly in senescent animals, particularly in the thalamus, where the mRNA became undetectable by RNA blot hybridization. This age-related pattern of expression suggests that the functions controlled by this gene may be lost with aging. Hybridization histochemistry revealed that the novel gene is selectively expressed in neurons and that its expression may be upregulated by gonadal steroids. Using a 3'-RACE RT-PCR approach we have now cloned the 3'-end of the MK-14 clone (approx. 300 bp), and are in the process of cloning the 5'-end of the cDNA by 5'-RACE PCR. In vitro studies using primary cell cultures of rat striatum, thalamus and frontal cortex, revealed that disruption of MK-14 gene expression by an anti-sense RNA, complementary to the monkey sequence, reduced dopamine D2 receptor gene expression without affecting the expression of other unrelated genes. These preliminary results suggest the MK-14 gene product may contribute to regulating D2 receptor expression. Molecular characterization of the entire MK-14 cDNA followed by additional in vitro and in vivo experiments will be required to substantiate this notion.